Presently about 6.8 M tons of soybean is produced in India and extracted for oil. The solvent extracted flour is exported to foreign countries for feed purposes. By providing additional facilities for the hygienic processing of soybean in the solvent extraction units, it is possible to obtain edible grade defatted flour having the desired functional characteristics. After the recovery of oil, 4.9 M tons of soy flour is available in India for utilization. A small portion of the total soybean produced also finds its use for different edible grade flours, protein isolate and texturized products. The popularity of these products are greatly increasing worldwide. Soybean - which contains about 40% protein - is an excellent source this complex substance. New manufacturing techniques for high quality soybean foods have been developed by lowering or destroying the anti-nutritional factors such as trypsin inhibitors.
U.S. Pat. No. 5,180,597 discloses a process for hydrolyzed vegetable protein with enhanced flavor, which contains no detectable level of monochlorodihydroxypropanol. In the above reference, wheat gluten is hydrolyzed using Prozyme 6 (a fungal protease) at a temperature of 40-50° C., pH 6.5-7.0, enzyme concentration of 0.1-2% of substrate for a time period of 4 h. The hydrolyzed protein is treated with gaseous HCl for deamidation before the addition of acid for inactivating the enzyme. The drawback in such hydrolysis is that it is likely to lead to racemisation of amino acids and the addition of acid increases the salt content in the product.
U.S. Pat. No. 5,077,062 discloses a low sodium, low mono sodium glutamate soy hydrolysate that is prepared from soy material such as soy flour, soy meal or soy grits using fungal protease in water. The hydrolysis is conducted in the absence of acid or base at 90° C. for 2 h. After deactivating the enzyme and de-watering the mixture, the resulting hydrolysate contains between 45 and 55 wt. % enzymatically hydrolysed soy based protein with an average molecular weight of 670,000±50,000. The fungal protease used is different from the enzyme used in the present invention. The process is energy intensive due to the high temperature (90° C.) used.
U.S. Pat. No. 4,757,007 discloses the preparation of two hydrolyzed products using a protease from soy protein. The soy protein is hydrolyzed with papain or pepsin after precipitating with alcohol. The drawback of the process is that it involves the separation of the mixture of hydrolyzed products. Hydrolysis is carried out using papain or pepsin. Acidification is carried out to bring down the pH to 2.5-5.0 to separate the two kinds of hydrolysates, which could lead to an increase in salt content.
European Patent No. 0148600 B1 relates to the preparation of hydrolyzed protein from protein isolate after jet cooking or dynamic heating at 104° C. for a few seconds and later cooling in a vacuum chamber before performing hydrolysis using bromelin. The protein was precipitated at its isoelectric point from an aqueous extract of the material before the hydrolysis. The drawback of the process is that the starting material protein isolate is more expensive. The process is a multi-step process, and is energy intensive. The process further needs machines like the jet cooker and a vacuum chamber.
European Patent No. 0223560 A2 discloses a method describing the separation of protein hydrolysates with meat and cheese, favor from proteinaceous feed stocks (e.g. containing soybean, gluten, whey, casein, hemoglobin, yeast, cereal or microbial proteins) by stepwise hydrolysis using an endopeptidase followed by amino peptidase from Streptococcus lactus. The drawback of the process is that it is a multi-step process.
European Patent No. 0087246 B1 discloses a process for the hydrolysis of soybeans, wheat gluten and cotton seeds using fungal protease from Aspergillus and pancreatin (trypsin, chymotrypsin A, B and C, elastase and carboxypeptidase A and B). Activated charcoal is used to treat the hydrolysate, which is used for nutritional improvement. The drawback of the process is that it involves more steps.
European Patent No. 0187048 A2 describes the preparation of soy protein hydrolysate with 0.25 to 2.5% degree of hydrolysis (DH) using microbial rennet (Mucor miehei) and to be used as an egg white substitute. The enzyme used in the process is different and involves very low DH of soy protein.
United Kingdom Patent No. 2053228A describes a process for the production of soy protein hydrolysate from partially defatted soy material by hydrolysis with proteolytic enzyme. The drawback of the process is that due to the partial defatting soy flour, remaining oil comes in contact with the protein phase, which could lead to off-flavors.
U.S. Pat. No. 4,324,805 describes a method for producing soy protein hydrolysate and oil from partially defatted soy material by hydrolysis with a proteolytic enzyme. The soyflour is partially defatted by water washing at pH 3.5-4.5 and later hydrolyzed using water and a base to increase the pH. The DH is in the range of 8-12%. Oil is recovered from the wash water. Alcalase is the enzyme used. The drawback of the process is that it is a multi step process and due to partial defatting of soy flour, remaining oil comes in contact with the protein phase which could lead to off-flavors. Enzyme inactivation is done by the addition of acid, which is likely to lead to increased salt content in the product.
U.S. Pat. No. 3,640,725 describes an enzymatic hydrolysis process for the production of soy protein hydrolysates. The soy seeds are comminuted and heated at 90-140° C. Protease (fungal and bacterial) is added at 25-75° C. The fiber is separated and slurry has two phases - an oil and an aqueous phase. The aqueous phase is brought to pH 4.5 to precipitate the protein, which is then concentrated. The starting material is not defatted and hence the residual oil could come in contact with the aqueous phase, which could lead to off-flavors.
Canadian Patent No. 905742 describes a soy protein hydrolysate modified with pepsin to yield a product which, in the presence of water and sugar, whips at a rapid rate to produce aerated products of low density.
European Patent No. 0797928A1 describes a process for the manufacture of a soy protein hydrolysate with a protease used selectively to decompose glycinin at a pH of 1.5-2.5. The pH used in the process is very low and therefore differs from the pH used in the present invention. Further, the aim of the process is to achieve a low glycinin content which is not the case in the present invention.
Reference may be made to a published paper entitled “Industrial production and application of soluble enzymatic hydrolysate of soy protein” (Olsen, H. S., Adler Nissen, J., [1979], Process Biochemistry, 14[7], 6,8, 10-11), wherein a method for preparation of soy protein hydrolysate from soy flakes washed at pH 4.5 followed by hydrolysis using alcalase is described. The solubility of the substrate is low at the acidic pH which is likely to result in low yields. The enzyme used is different from the enzyme used in the present invention.